B2600

DTC B2600

DIAGNOSTIC INSTRUCTIONS
- Perform the Diagnostic System Check - Vehicle
- Strategy Based Diagnosis
- Diagnostic Procedure Instructions Initial Inspection and Diagnostic Overview

DTC DESCRIPTOR

DTC B2600
Daytime Running Lamp Control Circuit




DIAGNOSTIC FAULT INFORMATION

CIRCUIT/SYSTEM DESCRIPTION
The low beam headlamps operate at reduced intensity when in daytime running lamps (DRL) mode. The ground circuit to the switch side of the DRL relay has a resistor in-line to reduce the intensity of the low beam headlamps for DRL operation. The body control module (BCM) receives a signal from the ambient light sensor indication a low or high ambient, outside light level. Under daylight conditions the BCM grounds the DRL relay control circuit energizing the DRL control relay soldered to the underhood fuseblock. The now closed relay supplies ground directly to the low beam headlamps and to the BCM on the headlamp low beam signal circuit. The low beam headlamps now illuminate with reduced intensity. The DRL relay is grounded within the BCM. Any time the headlamps are illuminated the DRL will not illuminate. Manual park lamps do not effect DRL operation.

CONDITIONS FOR RUNNING THE DTC
- The ignition switch is in the RUN position.
- The headlamp switch is in the AUTO position.
- The park brake is not applied.
- The gear selector is not in the PARK position.

CONDITIONS FOR SETTING THE DTC
- The DRL resistor supply voltage circuit is open, or shorted to ground.
- The headlamp low beam signal circuit between a headlamp and the Underhood fuse block is open or shorted to ground.
- The battery positive voltage circuit to the headlamp is open or shorted to ground.
- One of the headlamp fuses in the Underhood fuse block are open.
- The DRL resistor ground circuit is open.
- The DRL resistor is open or shorted.
- The DRL relay is stuck in the OPEN position.

ACTION TAKEN WHEN THE DTC SETS
The BCM turns off the DRL relay control for the remainder of the ignition cycle.

CONDITIONS FOR CLEARING THE DTC
- A current DTC B2600 clears when the BCM no longer detects a short to battery positive voltage in the control circuit on the park lamp relay.
- 100 consecutive ignition cycles have been recorded without the DTC being detected.
- Using a scan tool can clear the DTC.

DIAGNOSTIC AIDS
- Check both the LH and RH headlamps for proper operation
- Check both the LH High Beam, LH Low Beam and RH High Beam and RH Low Beam Head lamp fuses located in the underhood fuseblock.
- If DTC B2602 also sets, perform the diagnostics for DTC B2602 before performing diagnostics for DTC B2600 B2600

CIRCUIT/SYSTEM TESTING

DRL Relay Circuit Testing
1. Ignition OFF, disconnect the DRL PCB relay underhood fuseblock terminals C2 pin 38 coil side and underhood fuseblock terminal C3 pin 15 switch side.
2. Ignition ON, verify the DRLs are deactivated.
- If the DRLs are still activated, replace the underhood fuseblock.
3. Verify that a test lamp illuminates between the DRL PCB relay coil voltage supply circuit, check the underhood fuseblock terminal B+ feed of the underhood fuseblock and ground.
- If the test lamp does not illuminate, replace the underhood fuseblock. If the voltage supply circuit fuse is open, replace the underhood fuseblock.
4. Verify that a test lamp illuminates between the DRL PCB relay switch voltage supply circuit, check the underhood fuseblock B+ voltage feed supply circuit and ground.
- If the test lamp does not illuminate, replace the underhood fuseblock.
5. Connect a 15-amp fused jumper wire between the underhood fuseblock B+ feed and the relay switch control circuit underhood fuseblock terminal C2 pin 38. Verify the DRLs are activated.
- If the DRLs are not activated, replace the underhood fuseblock.
6. Connect a test lamp between the relay coil control circuit, underhoood fuseblock terminal C2 pin 38 and the relay coil voltage supply circuit, use the underhood fuseblock B+ feed terminal.
7. Command the DRL relay ON and OFF with a scan tool. The test lamp should turn ON and OFF when changing between the commanded states.
- If the test lamp remains ON all the time, test for a short to ground on the relay coil control circuit. If the circuit tests normal, replace the BCM.
- If the test lamp remains OFF all the time, test for a short to voltage or an open/high resistance on the relay coil control circuit. If the circuit tests normal, replace the BCM.
8. If all circuits test normal, test or replace the underhood fuseblock..

REPAIR INSTRUCTIONS
Perform the Diagnostic Repair Verification after completing the diagnostic procedure.
- Control Module References for BCM replacement, setup, and programming Programming and Relearning
- Underhood Electrical Center or Junction Block Replacement Verification Tests